1. Field of the Invention
The present invention relates to a monoazo metal compound, a composition comprising a monoazo metal compound, a toner for developing electrostatic images, a charge control agent for controlling or stabilizing the amount of charges of said toner, a powdery paint for electrostatic painting and a charge enhancer for enhancing the charge of said powdery paint.
2. Description of the Prior Art
In copying machines, printers and other instruments based on electrophotography, various toners containing a coloring agent, a fixing resin and other substances are used to visualize the electrostatic latent image formed on the photoreceptor having a light-sensitive layer containing an inorganic or organic photoconductive substance.
Toner chargeability is a key factor in electrostatic latent image-developing systems. Thus, to appropriately control or stabilize the amount of toner charge, a charge control agent providing a positive or negative charge is often added to the toner.
Of the conventional charge control agents in actual application, those providing a positive charge for a toner include basic dyes such as nigrosine dyes and triarylmethane dyes, and quaternary ammonium salts, i.e. electron donors. Charge control agents providing a negative charge for a toner include 2:1 type metal complexes of azo dyes and metal complexes of aromatic hydroxycarboxylic acids such as alkylsalicylic acids.
However, most metal complexes of azo dye structure used as charge control agents are usually unstable; for example, they are likely to be decomposed or deteriorated to lose their expected charge control capability when exposed to mechanical friction or impact, temperature or humidity changes, electric impact, light irradiation, etc. Also, even such metal complexes possessing a practically applicable charge providing property are often problematic as to charge stability or often contain impurity chemicals lacking charge control effect due to differences in production method etc., posing many problems regarding quality stability, reliability and other aspects.
Also, to improve paint adhesion efficiency in electrostatic powder painting, there have been attempts to apply charge control agents that have traditionally been used to control or enhance the charge of toners for developing electrostatic images.
Such attempts include an electrostatic powdery paint containing a resin polymer of an azine dye [Japanese Patent Unexamined Publication No. 67563/1985], a resin powder composition for electrostatic painting containing a charge enhancer like a metal-containing complex salt compound (Japanese Patent Unexamined Publication No. 75077/1988), and a powdery paint composition containing a quaternary ammonium salt as a charge control agent or charge enhancer (Japanese Patent Unexamined Publication No. 212563/1990).
However, these electrostatic powdery paints remain to be further improved in terms of environmental stability and heat resistance and durability under high-temperature conditions during powder painting.
Among charge control agents or charge enhancers capable of resolving these problems are the metal complex salt compounds of monoazo dyes, having the following structures: ##STR2## wherein A represents H, an alkali metal, an amine or the like.
Such chromium complex salt dyes are what is called 2:1 type azo-metal complex salt dyes wherein 2 molecules of a monoazo dye are coordinated to 1 trivalent chromium atom, and remain to be further improved as to chargeability stability and reliability.
The object of the present invention is to provide a metal compound of new chemical structure excellent in charge control or charge-enhancing property, heat resistance and light fastness; a charge control agent or charge enhancer that contains said metal compound as an active ingredient, that is good in dispersibility in resin and excellent in environmental resistance (stability of charge control or charge-enhancing property to changes in temperature or humidity), storage stability (stability over time of charge control or charge-enhancing property) and durability (charge control or charge-enhancing property stability in frequently repeated use), and that does not affect toner fixability or offset property when used in toners; and a toner for developing electrostatic images and powdery paint for electrostatic painting of stable quality and high reliability.